Oxidants, such as sodium hypochlorite, are routinely used to control microbial growth in paper making systems. Paper pulp, being a mass of wet cellulose and other materials, provides abundant opportunity for the growth of bacteria, fungi, and other microbes, so that a free chlorine-generating biocide is desirably added to the treated system.
While oxidants such as chlorine can provide adequate microbial control, they have a negative effect on optical brighteners, dyes, and the like which are added to the pulp. Also, chlorine that is released in the pulp can cause corrosion of nearby metal components of the processing machinery. The negative effects of chlorine can be reduced by using halogen stabilizers. While Sweeny U.S. Pat. No. 5,565,109 discloses a variety of organic halogen stabilizers, the effectiveness of the process has been unduly low, and the yield of stabilized chlorine species has been unduly low.
By this invention, an improvement is provided with respect to urea and derivatives thereof as a stabilizer of a free halogen source such as sodium or calcium hypochlorite. It has been found that at a pH that is greater than 10, the reaction yield is significantly improved, to provide stabilized halogen (particularly chlorine) in a treated system. Because of the stabilizing action of urea exerted on a free chlorine-generating biocide agent such as sodium hypochlorite, it has been found that improved microbial control can be provided, while minimizing or eliminating the undesirable impact of chlorine on other additives to the wet end of the paper process and the pulp, such as dyes and optical brightening agents. Also, less chlorine-generating agent is required to be added, because of its stabilized form and consequent more gradual release of chlorine, providing a greater antimicrobial effect for improved reduction of microorganisms such as planktonic and sessile bacteria. Also, corrosive effect upon the metal parts of the processing apparatus is reduced by the stabilization provided to free chlorine-generating materials, in accordance with this invention.